Functions for manipulating Pandoc documents or extracting
information from them by walking the Pandoc structure (or
intermediate structures like '[Block]' or '[Inline]'.
These are faster (by a factor of four or five) than the generic
functions defined in Text.Pandoc.Generic.

Here's a simple example, defining a function that replaces all the level 3+
headers in a document with regular paragraphs in ALL CAPS: